Bounded controllers for global path tracking control of unicycle-type mobile robots

• Global path tracking controllers are designed for mobile robots.
• The new one-step ahead backstepping method is introduced to design bounded controllers.
• The control torques are bounded with a predefined bound for all initial conditions.
• The tracking errors globally asymptotically and locally exponentially converge to zero.

This paper presents a design of bounded controllers with a predetermined bound for global path tracking control of unicycle-type mobile robots at the torque level. A new one-step ahead backstepping method is first introduced. The heading angle and linear velocity of the robots are then considered as immediate controls to force the position of the robots to globally and asymptotically track its reference path. These immediate controls are designed based on the one-step ahead backstepping method to yield bounded control laws. Next, the one-step ahead backstepping method is applied again to design bounded control torques of the robots with a pre-specified bound. The proposed control design ensures global asymptotical and local exponential convergence of the position and orientation tracking errors to zero, and bounded torques driving the robots. Experimental results on a Khepera mobile robot verify the proposed control controller.